The present invention relates to a lever control arrangement for controlling the movement of an oscillating lever.
Such an arrangement may particularly, though not exclusively, be applied to machines which are used to mount integrated-circuit chips on a flexible strip provided with interface conductors and also to machines which enable the chips so mounted to be soldered to an interconnecting base normally referred to as a substrate.
A machine of this kind is described and illustrated, for example, in U.S. Pat. No. 3,887,783 and includes a movable support mounted on sliders and provided at one of its ends with a soldering head. The movable support may be moved by means of a drive motor coupled to the movable support either via a rack-and-worm mechanism or via a cam and oscillating lever mechanism and arranged to enable the soldering head to be brought into contact with the articles to be soldered.
To obtain soldered joints of a high quality, it is necessary for adequate pressure to be exerted by the soldering head on the parts to be soldered during the soldering operation. Nevertheless, this pressure should not exceed a predetermined limiting value so as to prevent the substrates or the integrated circuit chips from being damaged as a result of excessive pressure. This is why, in such machines, it is necessary for the force with which the soldering head is pressed against the parts to be soldered to remain between two predetermined limiting values.
In the machine which forms the subject matter of the above-identified patent, this force is provided by a leaf spring which, providing as it does a connection between the rack and the support, becomes subject to deformation from the time when, the motor having been actuated to move the soldering head towards the articles to be soldered, the movement of the head is arrested by the said articles. However, this arrangement is not entirely satisfactory because the force with which the soldering head is pressed against the articles to be soldered depends upon the extent to which the leaf spring is deformed and it is difficult to adjust the amount of this deformation accurately so that the force in question will meet the condition hereinbefore stated. Also, given that in the machine in the above-identified patent the soldering head in the course of its movement also has to engage in a cutting die arranged in its path and, in order to detach the chip from the strip on which it was mounted, has to exert sufficient force to cut through the interface conductors of a chip which has previously been placed over the die, this arrangement requires extremely fine adjustments and thus proves particularly expensive.
The present invention seeks to overcome these disadvantages and provides a lever control arrangement which, in controlling the movement of an oscillating lever, allows the lever to exert a force of predetermined magnitude on an article placed in its path, which article may, for example, be formed by a movable support provided with a soldering head.